The invention relates to a bone plate and bone plate/fastener combination for fracture fixation and methods for using the same.
A large number of bone plates are known from the prior art. The vast majority of these plates are designed with a bottom side intended for surface contact with the bone. In contrast, the top side of the plate is not designed for this surface contact and usually has countersunk areas in the plate holes to better accommodate the heads of the bone screws. Because of the different features for the top and bottom surfaces of the bone plate, most prior art bone plates are asymmetrical with regard to their main middle plane, i.e. a plane extending between the top and bottom surfaces.
The disadvantages of these asymmetric bone plates include the fact that for optimal clinical results, the plate must be secured to the bone with the bottom surface in contact with the bone. However, clinical experience has shown that in the operating room, bone plates are occasionally applied to the bone with the wrong side facing the bone. Such errors are more likely to occur when working with bone plates having small dimensions and when the operating personnel are pressed for time.
French Patent No. 2,642,958 discloses a spinal bone plate that appears to have plate holes that are countersunk on both the top and bottom surfaces. However, the bone plate also appears to have a longitudinal curvature, and is therefore asymmetrical. French Patent No. 2,680,673 discloses another spinal bone plate. The bone plate, which also appears to have plate holes that are countersunk on both the top and bottom surfaces, contradicts the type of use given in the description for the lumbar spine, which would require an anatomical curvature of approximately 158xc2x0. The rectangular profile shown in both of these French patents is also not optimal for some clinical applications.
Thus, there exists a need for an improved bone plate.
The present invention is directed to a bone plate having first and second surfaces and at least one plate hole extending from the first surface to the second surface for receiving a fastener, such as a bone screw. The bone plate has a cross section that is preferably oval. The bone plate is substantially symmetrical about a middle plane extending between the first and second surfaces. Because the bone plate is substantially symmetrical, a first volume (Va) defined by a portion of the bone plate from the first surface to the middle plane and a second volume (Vb) defined by a portion of the bone plate from the second surface to the middle plane are configured and dimensioned such that Va/Vb is between about 0.98 and 1.02.
Advantageously, the plate holes can be cylindrical and round. Also, the plate holes may be narrower in a central portion and wider in end portions that extend toward the first and second surfaces, i.e. the plate holes are countersunk on each end. If the plate holes are countersunk, the end portions preferably have a conical shape toward the first and second surfaces. In an exemplary embodiment, the diameter of the plate holes in a direction parallel to the longitudinal axis of the bone plate is greater than the diameter in a direction perpendicular to the longitudinal axis. In this exemplary embodiment, the plate holes preferably have an oval shape.
In one embodiment, the first and second surfaces may be planar. In another embodiment, the first and second surfaces are advantageously concave along the longitudinal axis in an area between consecutive plate holes.
The bone screw can have a spherical head for slidingly engaging the plate holes. In order to lock the bone screw to the bone plate, the bone screw can have a thread engaging the plate holes.
The present invention also relates to a method for fixing a bone with a bone plate having first and second surfaces and at least one plate hole extending from the first surface to the second surface. A section of the bone plate is attached to a first portion of the bone such that the first surface of the bone plate faces the first portion of the bone. Another section is attached to a second portion of the bone such that the second surface of the bone plate faces the second portion of the bone.
In another method according to the present invention, a first portion of the bone plate is inserted into the medullary canal of the bone and a second portion of the bone plate is attached to the cortex of the bone. Because of the structure of the bone plate according to the present invention, either the first or second surface of the second portion can face the cortex of the bone.